My 7 year old loves Arianna Grande, this hits home in a particularly nasty way for me. Targeting little girls is just sick.
How can it be stopped? That's the scary thing.
It can't mate, not completely. I can become radicalised in my bedroom with a private VPN and never speak to anyone IRL about my thoughts. I can find the makings of explosives in household goods, or steal a lorry and drive onto the pavement. Even under a police state with armed checkpoints you still get terrorist attacks.
But they are just noisy and scary, they aren't a serious threat to our lives in general or our way of life generally. Just shit eating flies bothering the elephant of liberal democracy. You are still, even with this atrocity, more likely to die in a car crash or train derailment than going about your business at a concert or market and you wouldn't even think about letting that fact stop you driving or travelling by train.
They are sad, worthless pieces of shit desperate for some relevance in a world that's fast leaving them behind. We have the best armed and security services around IMO and we have been excellent at stopping them so far and driving them back where they originate. Any long term solution will be slow and multi-faceted, until then we just have to keep calm and carry on.